Dental polymerizable monomers

ABSTRACT

Provided are dental polymerizable monomers that can give cured products having high toughness and high rigidity, dental polymerizable monomer compositions containing the polymerizable monomers, and dental compositions containing the dental polymerizable monomer compositions, and cured products thereof having high mechanical properties. The dental polymerizable monomer (A) which includes a urethane acrylate obtained from an appropriately rigid diisocyanate and an appropriately flexible hydroxyacrylate is used to prepare a dental polymerizable monomer composition containing the dental polymerizable monomer, and a dental composition containing the dental polymerizable monomer composition.

TECHNICAL FIELD

The present invention relates to novel dental polymerizable monomers,dental polymerizable monomer compositions including the polymerizablemonomers, dental compositions including the dental polymerizable monomercompositions, and cured products obtained by curing the dentalcompositions.

BACKGROUND ART

Composite resins that are typical examples of dental compositionsusually contain polymerizable monomer compositions includingpolymerizable monomers and additives such as a filler, a polymerizationinitiator, a polymerization inhibitor and a dye. In a composite resinincluding such components, a filler usually has the largest weightfraction followed by a polymerizable monomer composition and these twocomponents represent a major proportion of the weight of the compositeresin. The polymerizable monomer composition serves as a binder for thefiller. The properties of the monomers, and the properties of curedproducts of the monomers are significantly influential on the propertiesand performance of the composite resin containing the monomercomposition, and cured products thereof.

From the points of view of aspects such as the biological safety ofmonomers and the mechanical strength and wear resistance of curedproducts, the polymerizable monomer compositions frequently includeradically polymerizable polyfunctional methacrylates. Typically, thepolyfunctional methacrylate compositions are based on2,2-bis[4-(3-methacryloyloxy-2-hydroxypropoxy)phenyl]propane(hereinafter, written as Bis-GMA) or2,2,4-trimethylhexamethylenebis(2-carbamoyloxyethyl) dimethacrylate(hereinafter, written as UDMA), and contain triethylene glycoldimethacrylate (hereinafter, written as TEGDMA) to control theviscosity.

In the dental clinical practice, the use of composite resins in therestoration of tooth defects has a long history and is still expanding.However, the mechanical properties of cured composite resins are stillinsufficient. In particular, the poor strength obstructs the applicationof the resins to sites subjected to a high stress, for example, the useas molar tooth crowning materials.

In recent years, clinical experts strongly demand the expansion of theuse of composite resins to such high-stress sites. Therefore, thedevelopment of composite resins having higher mechanical properties isan urgent necessity. As mentioned above, the properties of curedproducts of polymerizable monomer compositions used for composite resinssignificantly affect the properties of cured products of the compositeresins containing the compositions.

Techniques have been reported in which Bis-GMA and UDMA that are widelyused as main components of polymerizable monomer compositions arereplaced by other monomers so as to enhance the mechanical strength ofcured products of composite resins (Patent Literature 1 and PatentLiterature 2).

Further, techniques aiming to improve main component monomers have beenreported. For example, main component monomers are improved so as toenhance the refractive index of cured products of polymerizable monomercompositions (Patent Literature 3), and main component monomers areimproved so as to enhance the degree of polymerization shrinkage betweenbefore and after the curing of polymerizable monomer compositions(Patent Literature 4).

CITATION LIST Patent Literature

Patent Literature 1: JP-A-2000-204069

Patent Literature 2: JP-A-2013-544823

Patent Literature 3: JP-A-H11-315059

Patent Literature 4: WO 2012-157566

SUMMARY OF INVENTION Technical Problem

As already described, the expansion of the applications of dentalcompositions such as composite resins including polymerizable monomersinvolves a necessity of enhancements in the mechanical properties ofcured products of the dental compositions.

In view of the problems discussed above, objects of the presentinvention are to provide dental polymerizable monomers and dentalpolymerizable monomer compositions containing the polymerizable monomersthat can give cured products having high toughness and high rigidity,and to provide dental compositions containing such dental polymerizablemonomer compositions and cured products thereof having high mechanicalproperties.

Solution to Problem

The present inventors have found that a polymerizable monomercomposition containing a polymerizable monomer which includes a urethaneacrylate obtained from an appropriately rigid diisocyanate and anappropriately flexible hydroxyacrylate can give cured products havinghigh mechanical properties. After additional extensive studies, thepresent inventors have completed the present invention.

The present invention provides a dental polymerizable monomer, a dentalpolymerizable monomer composition including the polymerizable monomer, adental composition including the polymerizable monomer composition, anda cured product of the dental composition described in [1] to [8] below.

[1] A dental polymerizable monomer (A) including a urethane acrylatethat has at least one acryloyl group and is represented by the generalformula (1) below:

wherein in the general formula (1), R^(a) is a group which has adivalent C₆₋₉ aromatic hydrocarbon group or a divalent C₆₋₉ bridgedcyclic hydrocarbon group in the middle and is bonded to nitrogen atomsin adjacent carbamoyl groups via an unsubstituted methylene group; R^(b)and R^(c) are each independently a C₂₋₆ linear alkylene group or a C₂₋₆linear oxyalkylene group, each of which is optionally substituted with aC₁₋₃ alkyl group or a (meth)acryloylmethylene group in place of ahydrogen atom; and R^(d) represents a hydrogen atom or a methyl group.

[2] The dental polymerizable monomer (A) according to [1], wherein inthe general formula (1), R^(d) is a hydrogen atom.

[3] The dental polymerizable monomer (A) according to [1] or [2],wherein in the general formula (1), R^(a) is a group represented by theformula (2) or (3) below.

[4] The dental polymerizable monomer (A) according to [3], wherein inthe general formula (2), R^(a) is a group represented by the formula (4)below.

[5] The dental polymerizable monomer (A) according to any one of [1] to[4], wherein R^(b) and R^(c) in the general formula (1) independently ateach occurrence represents a C₂₋₆ linear alkylene group or a C₂₋₆ linearoxyalkylene group, each of which is optionally substituted with a C₁₋₃alkyl group in place of a hydrogen atom.

[6] A dental polymerizable monomer composition comprising the dentalpolymerizable monomer (A) described in any one of [1] to [5].

[7] The dental polymerizable monomer composition according to [6],wherein the viscosity at 25° C. is 1 to 100,000 mPa·s.

[8] A dental composition comprising the dental polymerizable monomercomposition described in [6] or [7], a polymerization initiator and afiller.

[9] A dental material obtained by curing the dental compositiondescribed in [8].

Advantageous Effects of Invention

The dental polymerizable monomer compositions containing the dentalpolymerizable monomers of the invention satisfy high rigidity and hightoughness when cured. Further, the dental polymerizable monomercompositions have an appropriate viscosity to exhibit excellentmiscibility with fillers. Thus, the compositions are useful for dentalcompositions containing components such as fillers.

The dental compositions containing the inventive dental polymerizablemonomer compositions can give cured products having high mechanicalproperties and are suited as, for example, composite resins forrestoring tooth crowns and artificial tooth materials, in particular.

DESCRIPTION OF EMBODIMENTS [Dental Polymerizable Monomer (A)]

The dental polymerizable monomer (A) of the invention includes aurethane acrylate having at least one acryloyl group represented by thegeneral formula (1) below.

In the general formula (1), R^(b) and R^(c) are each independently aC₂₋₆ linear alkylene group or a C₂₋₆ linear oxyalkylene group, each ofwhich is optionally substituted with a C₁₋₃ alkyl group or a(meth)acryloyloxymethylene group in place of a hydrogen atom; and R^(d)represents a hydrogen atom or a methyl group.

In a preferred embodiment, R^(b) and R^(c) in the general formula (1)are each a C₂₋₄ linear alkylene group or a C₂-4 oxyalkylene group ineach of which any hydrogen atom may be substituted by a C₁₋₃ alkylgroup.

Examples of the linear alkylene groups include —CH₂CH₂—, —CH₂CH₂CH₂—,—CH₂CH₂CH₂CH₂—, —CH₂CH₂CH₂CH₂CH₂— and —CH₂CH₂CH₂CH₂CH₂CH₂—. Of these,preferred linear alkylene groups are, for example, —CH₂CH₂—, —CH₂CH₂CH₂—and —CH₂CH₂CH₂CH₂—.

Examples of the linear oxyalkylene groups include —CH₂CH₂OCH₂CH₂— and—CH₂CH₂OCH₂CH₂OCH₂CH₂—. Of these, a preferred linear oxyalkylene groupis, for example, —CH₂CH₂OCH₂CH₂—.

To ensure that the dental polymerizable monomer (A) will exhibitappropriate flexibility, the linear alkylene groups or the linearoxyalkylene groups each usually have 2 to 6 carbon atoms, preferably 2to 4 carbon atoms, and more preferably 2 carbon atoms.

Examples of the alkyl groups which may substitute for hydrogen atoms inthe linear alkylene groups or the linear oxyalkylene groups includeCH₃—, CH₃CH₂—, CH₃CH₂CH₂— and (CH₃)₂CH—. To ensure that the dentalpolymerizable monomer (A) will exhibit appropriate flexibility, thealkyl groups preferably have 1 to 3 carbon atoms, more preferably 1 to 2carbon atoms, and still more preferably 1 carbon atom.

Examples of the (meth)acryloyloxymethylene groups which may substitutefor hydrogen atoms in the linear alkylene group or the linearoxyalkylene group include methacryloyloxymethylene group andacryloyloxymethylene group.

Of the urethane acrylates represented by the general formula (1), thoseurethane acrylates which are represented by the general formula (1′)below are preferable in order to obtain the advantageous effects of theinvention more effectively.

The definitions, specific examples and preferred examples of R^(a),R^(b) and R^(c) in the general formula (1′) are the same as those ofR^(a), R^(b) and R^(c) in the general formula (1).

Here, the dental polymerizable monomer (A) represented by the generalformula (1) has at least one acryloyl group at an end position. Theurethane acrylate represented by the general formula (1′) according to apreferred embodiment of the dental polymerizable monomer (A) has atleast two acryloyl groups at both end positions.

When substituents in R^(b) and R^(c) are (meth)acryloyloxymethylenegroups and the (meth)acryloyloxymethylene groups are theacryloyloxymethylene groups, the polymerizable groups present in thedental polymerizable monomer (A) are all the acryloyl groups.

When, on the other hand, substituents in R^(b) and R^(c) are(meth)acryloyloxymethylene groups and the substituents do not meet theabove configuration, the polymerizable groups present in the dentalpolymerizable monomer (A) include both the acryloyl groups and themethacryloyl groups.

In order to obtain cured products having excellent toughness, it ispreferable that when the dental polymerizable monomer (A) contains threeor more polymerizable groups, the polymerizable groups include a smallernumber of methacryloyl groups and a larger number of acryloyl groups. Itis more preferable that the polymerizable groups be all the acryloylgroups (the (meth)acryloyloxymethylene groups which can be present asthe substituents in R^(b) and R^(c) be the acryloyloxymethylene groups).

The substituent in R^(b) and R^(c) preferably substitutes for a hydrogenatom on the carbon atom that is adjacent to the carbon atom in thelinear alkylene group or the linear oxyalkylene group that is adjacentto the acryloyl group present at both end positions of the dentalpolymerizable monomer (A). When, for example, the linear alkylene groupis —CH₂CH₂—, compounds represented by the general formula (5) arepreferable.

The number of the alkyl groups substituting for hydrogen atoms and the(meth)acryloyloxymethylene groups substituting for hydrogen atoms ispreferably 0 to 8, although not particularly limited thereto. To ensurethat the dental polymerizable monomer (A) will exhibit appropriateflexibility, it is more preferable that the number of such substituentsbe 0 to 4, still more preferably 0 to 2, and particularly preferably 0,namely, no such substituents.

In the general formula (1) or (1′), R^(a) is a group bonded to nitrogenatoms in two adjacent carbamoyl groups, and has a divalent aromatichydrocarbon group or a divalent bridged cyclic hydrocarbon group in themiddle and has two methylene groups which are each unsubstituted andbonded to the nitrogen atom in the carbamoyl group and to the divalentgroup (hereinafter, such methylene group is also written as themethylene group A).

To ensure appropriate rigidity, the divalent aromatic hydrocarbon groupor the divalent bridged cyclic hydrocarbon group in R^(a) usually has 6to 9 carbon atoms, and preferably 6 to 7 carbon atoms. Examples of thearomatic hydrocarbon groups or the bridged cyclic hydrocarbon groupshaving 6 to 7 carbon atoms include phenylene group andbicyclo[2.2.1]heptylene group. Of these, bicyclo[2.2.1]heptylene groupis preferred from the point of view of the toughness of the curedproduct.

When the group in R^(a) that is bonded to the two methylene groups A isthe aromatic hydrocarbon group, the two methylene groups A may bepresent at ortho positions, meta positions or para positions withrespect to each other on the benzene ring in the aromatic hydrocarbongroup. To obtain the advantageous effects of the invention, it ispreferable that these two methylene groups A be present at metapositions or para positions with respect to each other, and morepreferably at meta positions with respect to each other.

When the group in R^(a) that is bonded to the two methylene groups A isthe bridged cyclic hydrocarbon group, the two methylene groups A may bepresent at any positions with respect to each other on the carbon ringin the bridged cyclic hydrocarbon group. To obtain the advantageouseffects of the invention, it is preferable that these two methylenegroups A be not bonded to the same carbon atom in the carbon ring, andit is more preferable that these methylene groups A be bonded torespective carbon atoms in the carbon ring that are separate from eachother through two or more carbon atoms in the carbon ring.

The regioisomers differing in the positions of these two methylenegroups A may be used singly, or two or more kinds of such isomers may beused as a mixture.

Specifically, R^(a) is preferably a group selected from those groupsrepresented by the general formulas (2) and (3) below. In the case ofthe group represented by the general formula (2), the group may bederived from a mixture of regioisomers differing in the positions of themethylene groups, or may be derived from any single type of aregioisomer isolated. In particular, the group represented by thegeneral formula (4) is more preferable. In the case of the grouprepresented by the general formula (3), the group is generally derivedfrom a mixture of regioisomers having the methylene groups at2,5-positions or 2,6-positions.

Of the dental polymerizable monomers (A) that are urethane acrylates,those urethane acrylates represented by the following chemical formulasare preferable.

In the above formulas, Et indicates an ethyl group.

The molecular weight of the dental polymerizable monomer (A) depends onthe structure, but is generally about 400 to 1000, and preferably 400 to700. When the molecular weight is in this range, the monomer exhibits alow viscosity to provide an advantage in the preparation of a dentalcomposition.

Further, the dental polymerizable monomer (A) is preferably liquid atroom temperature. The viscosity of the dental polymerizable monomer (A)at 65° C. is preferably 1 to 50000 mPa·s, more preferably 1 to 20000mPa·s, and still more preferably 1 to 5000 mPa·s. When the viscosity isin this range, the dental polymerizable monomer composition exhibits alow viscosity to provide an advantage in the preparation of a dentalcomposition. The dental polymerizable monomer (A) sometimes containsminor components other than the desired dental polymerizable monomer(A), such as oligomers formed during storage at high temperatures andhighly viscous byproduct compounds. However, the presence of such minorcomponents tends to be an insignificant problem in the use of a dentalcomposition as long as the viscosity is in the aforementioned range. Theviscosity is a value measured at 65° C. with a cone-plate viscometer(for example, TVE-22H manufactured by TOKI SANGYO CO., LTD.).

The dental polymerizable monomers (A) may be used singly, or two or moremay be used in combination.

Because of the inventive dental polymerizable monomer compositioncontaining the dental polymerizable monomer (A) that is the urethaneacrylate as described above, cured products of the compositions achieveboth toughness and rigidity.

The detailed reasons as to why the compositions can give cured productshaving such characteristics are not fully understood. The dentalpolymerizable monomer (A) is a urethane acrylate composed of a moietythat is derived from the diisocyanate (a2), as illustrated in, forexample, the general formula (8) discussed later, and includes aspecific divalent aromatic hydrocarbon group or a specific divalentbridged cyclic hydrocarbon group and methylene groups (for example,R^(a) in the general formula (1) or (1′)) (hereinafter, this moiety isalso written as the core); moieties derived from the alkylene chain inthe linear portion of the hydroxyacrylate (a1) (for example, R^(b) andR^(c) in the general formula (1) or (1′), or R^(d) in the generalformula (6) described later) (hereinafter, these moieties are alsowritten as the arms); carbamoyl groups connecting the arms to the core;and at least one acryloyl group (preferably, at least two acryloylgroups at both ends).

To ensure that cured products exhibit both toughness and rigidity, it isprobably necessary that the balance between a hard segment and a softsegment in (the molecule of) a polymerizable monomer be controlledappropriately.

In the case of, for example,2,2,4-trimethylhexamethylenebis(2-carbamoyloxyethyl) dimethacrylate(UDMA) that is used frequently in the conventional techniques, the2,2,4-trimethylhexamethylene group corresponding to the core in theinvention is a C₆ linear alkylene group substituted with methyl groupsand thus can be considered as a soft segment. The arms are ethylenegroups, which can be similarly considered to be soft segments.Accordingly, UDMA has no hard segments in the molecule except thecarbamoyl groups, and the molecule as a whole lacks rigidity.Consequently, cured products of dental polymerizable monomercompositions based on UDMA exhibit poor rigidity.

In contrast, the arms in the dental polymerizable monomer (A) in theinvention are alkylene chains having appropriate flexibility and can beconsidered as soft segments, while the core is such that a divalentaromatic hydrocarbon group (typically, an aromatic hydrocarbon grouphaving 6 to 9 carbon atoms) or a divalent bridged cyclic hydrocarbongroup (typically, a bridged cyclic hydrocarbon group having 6 to 9carbon atoms) is bonded to carbamoyl groups via an unsubstitutedmethylene group. Thus, the core can be considered as a hard segmenthaving appropriate rigidity. With this appropriate balance (structuralcharacteristics) between the soft segments and the hard segment, thedental polymerizable monomer (A) will exhibit appropriate rigidity.Thus, it is assumed that such molecules will give cured products havinghigher rigidity than is obtained with UDMA.

While the polymerizable groups in conventional dental polymerizablemonomers are frequently methacryloyl groups, the dental polymerizablemonomer (A) that is a urethane acrylate in the invention contains anacryloyl group as the polymerizable group (has at least one acryloylgroup, and preferably two acryloyl groups in the molecule). As mentionedhereinabove, it is probably necessary that the balance between a hardsegment and a soft segment in a polymerizable monomer should becontrolled appropriately in order for cured products of thepolymerizable monomers to satisfy both toughness and rigidity. Ingeneral, the comparison of properties of cured products frommethacrylate monomers and acrylate monomers having similar structuresshows that the methacrylate monomers give rigid cured products ascompared to cured products of the acrylate monomers. This fact indicatesthat the main chains formed by the polymerization of methacryloyl groupsbehave more like hard segments than soft segments, and the vice versafor the main chains resulting from the polymerization of acryloylgroups. Thus, it is assumed that the dental polymerizable monomer (A) inthe invention will give cured products having higher toughness thanthose from similar compounds having the methacryloyl groups alone. Forthe same reason, it is assumed that when the dental polymerizablemonomer (A) has more than two polymerizable groups, the obtainable curedproducts will exhibit higher toughness with a smaller number ofmethacryloyl groups and a larger number of acryloyl groups.

The dental polymerizable monomer (A) that is a urethane acrylate isobtained by reacting a hydroxy(meth)acrylate including an appropriatelyflexible hydroxyacrylate (a1) represented by the general formula (6)below with an appropriately rigid diisocyanate (a2) represented by thegeneral formula (8) below.

In the general formula (6), R^(f) represents a C₂₋₆ linear alkylenegroup or a C₂₋₆ linear oxyalkylene group, each of which is optionallysubstituted with a C₁₋₃ alkyl group or a (meth)acryloyloxymethylenegroup in place of a hydrogen atom.

In a preferred embodiment, R^(f) in the general formula (6) is a C₂₋₄linear alkylene group or a C₂₋₄ oxyalkylene group in which any hydrogenatom may be substituted by a C₁₋₃ alkyl group.

Examples of the linear alkylene groups include —CH₂CH₂—, —CH₂CH₂CH₂—,—CH₂CH₂CH₂CH₂—, —CH₂CH₂CH₂CH₂CH₂— and —CH₂CH₂CH₂CH₂CH₂CH₂—. Of these,preferred linear alkylene groups are, for example, —CH₂CH₂—, —CH₂CH₂CH₂—and —CH₂CH₂CH₂CH₂—.

Examples of the linear oxyalkylene groups include —CH₂CH₂OCH₂CH₂— and—CH₂CH₂OCH₂CH₂OCH₂CH₂—. Of these, a preferred linear oxyalkylene groupis, for example, —CH₂CH₂OCH₂CH₂—.

To ensure that the dental polymerizable monomer (A) will exhibitappropriate flexibility, the linear alkylene group or the linearoxyalkylene group usually has 2 to 6 carbon atoms, preferably 2 to 4carbon atoms, and more preferably 2 carbon atoms.

Examples of the alkyl groups which may substitute for hydrogen atoms inthe linear alkylene group or the linear oxyalkylene group include CH₃—,CH₃CH₂—, CH₃CH₂CH₂— and (CH₃)₂CH—. To ensure that the dentalpolymerizable monomer (A) will exhibit appropriate flexibility, thealkyl groups preferably have 1 to 3 carbon atoms, more preferably 1 to 2carbon atoms, and still more preferably 1 carbon atom.

Examples of the (meth)acryloyloxymethylene groups which may substitutefor hydrogen atoms in the linear alkylene group or the linearoxyalkylene group include methacryloyloxymethylene group andacryloyloxymethylene group.

Here, the hydroxyacrylate (a1) represented by the general formula (6)has an acryloyl group. Thus, the dental polymerizable monomer (A) alwayshas at least one acryloyl group at a molecular terminal.

When a substituent(s) in R^(f) is (are) (meth)acryloyloxymethylenegroup(s) and the (meth)acryloyloxymethylene group(s) is (are) theacryloyloxymethylene group(s), the polymerizable groups present in thehydroxyacrylate (a1) are all the acryloyl groups.

When, on the other hand, a substituent(s) in R^(f) is (are) a(meth)acryloyloxymethylene group(s) and the substituent(s) does (do) notmeet the above configuration, the polymerizable groups present in thehydroxyacrylate (a1) include both the acryloyl group(s) and themethacryloyl group(s).

In order to obtain cured products having excellent toughness, it ispreferable that when the hydroxyacrylate (a1) contains a plurality ofpolymerizable groups, the polymerizable groups include a smaller numberof methacryloyl groups and a larger number of acryloyl groups. It ismore preferable that the polymerizable groups be all the acryloyl groups(the (meth)acryloyloxymethylene groups which can be present as thesubstituents in R^(f) be the acryloyloxymethylene groups).

The substituent in R^(f) preferably substitutes for a hydrogen atom onthe carbon atom that is adjacent to the carbon atom in the linearalkylene group or the linear oxyalkylene group that is adjacent to theacryloyl group present in the hydroxyacrylate (a1). When, for example,the linear alkylene group is —CH₂CH₂—, compounds represented by thegeneral formula (7) are preferable.

The number of the alkyl groups substituting for hydrogen atoms and the(meth)acryloyloxymethylene groups substituting for hydrogen atoms ispreferably 0 to 4, although not particularly limited thereto. To ensurethat the dental polymerizable monomer (A) will exhibit appropriateflexibility, it is more preferable that the number of such substituentsbe 0 to 2, still more preferably 0 to 1, and particularly preferably 0,namely, no such substituents.

The hydroxyacrylates (a1) may be used singly, or two or more may be usedin combination. When reacted with a diisocyanate (a2) described later,the hydroxyacrylate (a1) may be used as a mixture with ahydroxymethacrylate.

The diisocyanate (a2) has a structure represented by the general formula(8) below:

R^(e) is a divalent C₆₋₉ aromatic hydrocarbon group or a divalent C₆₋₉bridged cyclic hydrocarbon group. To ensure appropriate rigidity, thearomatic hydrocarbon group or the bridged cyclic hydrocarbon groupusually has 6 to 9 carbon atoms, and preferably 6 to 7 carbon atoms.Examples of the aromatic hydrocarbon groups or the bridged cyclichydrocarbon groups having 6 to 7 carbon atoms include phenylene groupand bicyclo[2.2.1]heptylene group. Of these, bicyclo[2.2.1]heptylenegroup is preferred from the point of view of the toughness of the curedproduct.

When R^(e) is the aromatic hydrocarbon group, the two methylene groupsdirectly bonded to R^(e) may be present at ortho positions, metapositions or para positions with respect to each other on the benzenering in the aromatic hydrocarbon group. To obtain the advantageouseffects of the invention, it is preferable that these two methylenegroups be present at meta positions or para positions with respect toeach other, and more preferably at meta positions with respect to eachother.

When R^(e) is the bridged cyclic hydrocarbon group, the two methylenegroups directly bonded to R^(e) may be present at any positions withrespect to each other on the carbon ring in the bridged cyclichydrocarbon group. To obtain the advantageous effects of the invention,it is preferable that these two methylene groups be not bonded to thesame carbon atom in the carbon ring, and it is more preferable thatthese methylene groups directly bonded to R^(e) be bonded to respectivecarbon atoms in the carbon ring that are separate from each otherthrough two or more carbon atoms in the carbon ring.

The regioisomers differing in the positions of these two methylenegroups bonded to R^(e) may be used singly, or two or more kinds of suchisomers may be used as a mixture.

Specifically, the diisocyanate (a2) is preferably at least one compoundselected from those compounds represented by the general formulas (9)and (10) below. The compound represented by the general formula (9) maybe a mixture of regioisomers differing in the positions of the methylenegroups, or may be any single type of a regioisomer isolated. Inparticular, the compound represented by the general formula (11) is morepreferable. The compound represented by the general formula (10) iscalled bis(isocyanatomethyl)bicyclo[2.2.1]heptane and is generally amixture of regioisomers having the methylene groups at 2,5-positions or2,6-positions.

The diisocyanates (a2) may be used singly, or two or more may be used incombination.

As described hereinabove, the dental polymerizable monomer (A) of theinvention can be obtained, for example, by reacting ahydroxy(meth)acrylate(s) including the hydroxyacrylate (a1) with thediisocyanate (a2). The reaction may be performed by a known method or amethod in accordance with a known method.

For example, the dental polymerizable monomer (A) of the invention maybe obtained by mixing the hydroxyacrylate (a1) with the diisocyanate(a2). During this process, the hydroxyl groups in the hydroxyacrylate(a1) react with the isocyanate groups in the diisocyanate (a2) to formthe carbamoyl groups. This reaction is sometimes called theurethane-forming reaction.

The reaction may be performed in the presence or absence of a catalyst.To enhance the reaction rate, a catalyst is preferably added. Knowncatalysts capable of accelerating the urethane-forming reaction may beused as the catalysts.

Examples of the urethane-forming catalysts include organotin compoundssuch as dibutyltin dilaurate, dibutyltin dioctoate and tin octanoate;organic compounds of metals other than tin such as copper naphthenate,cobalt naphthenate, zinc naphthenate, acetylacetonatozirconium,acetylacetonatoiron and acetylacetonatogermanium; amine compounds andsalts thereof such as triethylamine, 1,4-diazabicyclo[2.2.2]octane,2,6,7-trimethyl-1-diazabicyclo[2.2.2]octane,1,8-diazabicyclo[5.4.0]undecene, N,N-dimethylcyclohexylamine, pyridine,N-methylmorpholine, N,N,N′,N′-tetramethylethylenediamine,N,N,N′,N′-tetramethyl-1,3-butanediamine,N,N,N′,N′-pentamethyldiethylenetriamine,N,N,N′,N′-tetra(3-dimethylaminopropyl)-methanediamine,N,N′-dimethylpiperazine and 1,2-dimethylimidazole; and trialkylphosphinecompounds such as tri-n-butylphosphine, tri-n-hexylphosphine,tricyclohexylphosphine and tri-n-octylphosphine.

Of these, dibutyltin dilaurate and tin octanoate are advantageous inthat the reaction is facilitated with a small amount of the catalyst andthe catalyst has high selectivity with respect to diisocyanatecompounds. When the urethane-forming catalyst is used, the amountthereof is preferably 0.001 to 0.5 wt %, more preferably 0.002 to 0.3 wt%, still more preferably 0.01 to 0.3 wt %, further preferably 0.01 to0.2 wt %, and still further preferably 0.05 to 0.2 wt % relative to thetotal weight of the hydroxyacrylate (a1) and the diisocyanate (a2) takenas 100 wt %. If the amount is below the lower limit, the catalyticeffect is decreased to give rise to a risk that a significantly longreaction time is incurred. If the amount is above the upper limit, thecatalytic effect is so increased that the reaction generates a largeamount of heat possibly to make it difficult to control the temperature.The catalyst may be added in the whole amount at the initiation of thereaction, or may be added successively or in portions to the reactionsystem as required. Such successive or portionwise addition of thecatalyst prevents the generation of an excessively large amount ofreaction heat at the initial stage of the reaction and thus facilitatesthe control of the reaction temperature.

The reaction temperature is not particularly limited, but is preferably0 to 120° C., more preferably 20 to 100° C., and still more preferably40 to 80° C. At a reaction temperature below the lower limit, thereaction rate is markedly decreased and the reaction requires a verylong time to complete or does not complete at times. On the other hand,the reaction at a temperature above the upper limit may involve sidereactions generating impurities. Such impurities may cause thecoloration of the acrylate compound produced.

To ensure stable production at the aforementioned preferred range oftemperatures, it is preferable that the reaction temperature becontrolled. The urethane-forming reaction is usually exothermic. In thecase where the reaction generates a large amount of heat and thetemperature of the reaction product may be elevated above the preferredrange of the reaction temperature, cooling is sometimes performed. Whenthe reaction has substantially completed and the temperature of thereaction product may be decreased below the preferred range of thereaction temperature, heating is sometimes performed.

The dental polymerizable monomer (A) has polymerization activity. Thus,undesired polymerization reaction may take place when the system issubjected to a high temperature during its production. To prevent suchundesired polymerization reaction, a known polymerization inhibitor maybe added before the initiation of the reaction or during the reaction.The polymerization inhibitor is not particularly limited as long as theinhibitor can suppress the reaction of the acrylate groups during theproduction of the dental polymerizable monomer (A). Examples thereofinclude dibutylhydroxytoluene (BHT), hydroquinone (HQ), hydroquinonemonomethyl ether (MEHQ) and phenothiazine (PTZ). Of these polymerizationinhibitors, BHT is particularly preferable because the consumption ofthe inhibitor by the reaction with the isocyanate groups is small ascompared to other phenolic polymerization inhibitors and also becausethe coloration encountered with amine polymerization inhibitors issmall. The amount of the polymerization inhibitor added is notparticularly limited, but is preferably 0.001 to 0.5 wt %, morepreferably 0.002 to 0.3 wt %, still more preferably 0.005 to 0.3 wt %,further preferably 0.005 to 0.1 wt %, and still further preferably 0.01to 0.1 wt % relative to the total weight of the hydroxyacrylate (a1) andthe diisocyanate (a2) taken as 100 wt %. If the amount is below thelower limit, the polymerization inhibitor may fail to perform asexpected. If the amount is above the upper limit, a dental compositioncontaining such a dental polymerizable monomer (A) may exhibit amarkedly low curing rate and may have a limited practical applicability.

The urethane-forming reaction may involve a solvent. The solvent is notparticularly limited as long as the solvent does not have practicalreactivity with respect to the hydroxyacrylate (a1) and the diisocyanate(a2), does not inhibit the reaction, and can dissolve the raw materialsand the product. The reaction may be performed in the absence ofsolvents. The hydroxyacrylate (a1) is usually a low viscous liquid andis miscible with the diisocyanate (a2) to allow the reaction to takeplace without solvents.

The hydroxyacrylate (a1) and the diisocyanate (a2) may be mixed witheach other by any methods without limitation. For example, a controlledamount of the diisocyanate (a2) may be admixed with the hydroxyacrylate(a1) placed in a reaction vessel; a controlled amount of thehydroxyacrylate (a1) may be admixed with the diisocyanate (a2) placed ina reaction vessel; or controlled amounts of the hydroxyacrylate (a1) andthe diisocyanate (a2) may be added to a reaction vessel at the same timeand mixed with each other. By these mixing methods, the amount of heatgenerated by the urethane-forming reaction can be controlled in anappropriate range and thus the temperature control during the reactionis facilitated. Alternatively, the urethane-forming reaction may beperformed in such a manner that the whole amounts of the hydroxyacrylate(a1) and the diisocyanate (a2) are added to a reaction vessel andthereafter the temperature is increased. During the reaction, thereaction temperature may be sharply increased due to the generation ofreaction heat and the temperature control by cooling may beappropriately required at times.

Oxygen is effective as a polymerization inhibitor for compoundscontaining acryloyl groups. Thus, oxygen is sometimes introduced intothe reactor to prevent undesired polymerization of acryloyl groupsduring the reaction. For example, oxygen may be introduced into thereactor in such a form as dried air or oxygen gas. Preferably, dried airis introduced into the reactor. For example, the dried air may beobtained by removing water using a known drying method such as the useof a condensing air dryer. In an embodiment, a mixed gas includingoxygen and an inert gas such as nitrogen may be introduced into thereactor. The use of such a mixed gas including oxygen and an inert gassuch as nitrogen is preferable similarly to the use of the dried air.The mixed gas including oxygen and an inert gas such as nitrogen may beobtained by mixing oxygen gas or the dried air containing oxygen with aprescribed amount of nitrogen. Here, nitrogen is preferably one that hasbeen dehydrated by a known drying method. The method for theintroduction is not particularly limited. For example, the gas may beintroduced in the form of bubbles from the bottom of the reaction vesselcontinuously or intermittently. Alternatively, the gas may be introducedcontinuously or intermittently to the space at the top of the reactionvessel. The rate of the introduction of dried air may be determinedappropriately in accordance with factors such as the size of thereaction vessel. When, for example, the volume of the reaction vessel is1 L, the introduction rate is usually 1 to 500 ml/min, and preferably 1to 300 ml/min. If the rate is below 1 ml/min, oxygen cannot beintroduced in a sufficient amount and may fail to serve as thepolymerization inhibitor. If the rate is above 500 ml/min, thevolatilization of the diisocyanate during the reaction is increased andthe properties of the dental polymerizable monomer (A) after curing maybe deteriorated.

If water is present as an impurity in the system during theurethane-forming reaction, the diisocyanate (a2) and water can reactwith each other to form impurities having a higher molecular weight thanthe target product. The increase in the amount of such impuritiesdisadvantageously causes the increase in the viscosity of the product.Thus, it is preferable that as little water as possible be present inthe reaction system during the urethane-forming reaction.

From the above aspect, the amount of water present in thehydroxyacrylate (a1) is preferably as small as possible. Specifically,the amount of water is preferably not more than 0.5 wt %, morepreferably not more than 0.3 wt %, and still more preferably not morethan 0.1 wt % relative to the hydroxyacrylate (a1). In the case wherethe hydroxyacrylate (a1) contains water in an amount exceeding the upperlimit, it is preferable that the hydroxyacrylate be used as a rawmaterial for the dental polymerizable monomer (A) that is a urethaneacrylate after water is removed therefrom by a known method. Thereaction vessel in which the urethane-forming reaction will be performedis preferably dried by a known method to remove water therefrom.

[Dental Polymerizable Monomer Compositions]

The dental polymerizable monomer composition of the invention containsthe dental polymerizable monomer (A) that is the urethane acrylate, andfurther contains an additional polymerizable compound.

The dental polymerizable monomer composition may contain a single kindof the dental polymerizable monomers (A), or may contain a mixture oftwo or more kinds thereof. For example, the dental polymerizable monomercomposition will contain two or more kinds of the dental polymerizablemonomers (A) when the dental polymerizable monomers (A) are preparedusing two or more kinds of hydroxyacrylates (a1), and a diisocyanate(s)(a2) as the raw materials, or when the dental polymerizable monomers (A)are prepared using a mixture of a hydroxyacrylate (a1) and ahydroxymethacrylate, and a diisocyanate(s) (a2) as the raw materials.

As such an additional polymerizable compound to be contained, preferredis a polymerizable compound (B) having at least one polymerizable groupselected from methacryloyl groups and acryloyl groups (the polymerizablecompound (B) differing from the dental polymerizable monomer (A)).

[Polymerizable Compound (B)]

The number of the polymerizable groups present in the polymerizablecompound (B) may be 1, or may be 2 or greater. The number of thepolymerizable groups is preferably 2 to 10. The number of thepolymerizable groups is more preferably 2 to 6. The number of thepolymerizable groups is still more preferably 2 to 4. The polymerizablecompound (B) may be composed of one kind of compound, or may be composedof a mixture of two or more kinds of compounds.

The molecular weight of the polymerizable compound (B) is preferably 80to 1000, and more preferably 150 to 700. If the molecular weight isbelow this range, the compound has a low boiling point. Thus, the abovelower limit is advantageous from the point of view of handlingproperties in the preparation of a dental composition. If the molecularweight is higher than the above range, the compound tends to exhibit ahigh viscosity. Thus, the above upper limit is advantageous from thepoint of view of handling properties in the preparation of a dentalcomposition.

The polymerizable compound (B) is preferably liquid at room temperature.The viscosity of the polymerizable compound (B) at 65° C. is preferably1 to 50000 mPa·s, more preferably 1 to 20000 mPa·s, still morepreferably 1 to 5000 mPa·s, and particularly preferably 1 to 3000 mPa·s.When the viscosity is in this range, the dental polymerizable monomercomposition exhibits a low viscosity to provide an advantage in thepreparation of a dental composition. Further, the viscosity of thepolymerizable compound (B) at 65° C. is preferably lower than theviscosity of the dental polymerizable monomer (A) at 65° C. Thepolymerizable compound (B) sometimes contains minor components otherthan the desired polymerizable compound (B), such as oligomers formedduring storage at high temperatures. However, the presence of such minorcomponents tends to be an insignificant problem in the use of a dentalcomposition as long as the viscosity is in the aforementioned range. Theviscosity is a value measured at 65° C. with a cone-plate viscometer.

Examples of the polymerizable compounds (B) having one polymerizablegroup include those polymerizable compounds represented by the generalformula (12) below.

In the general formula (12), R¹ is hydrogen or a methyl group, and R² isa C₁₋₂₀ monovalent organic group which may contain oxygen or nitrogen.

Examples of the monovalent organic groups include hydrocarbon groupssuch as C₁₋₂₀ acyclic hydrocarbon groups, for example, alkyl groups,alkenyl groups and alkynyl groups, and C₁₋₂₀ cyclic hydrocarbon groups,for example, cycloalkyl groups, cycloalkenyl groups, cycloalkynyl groupsand aryl groups; and C₁₋₂₀ oxygen-containing hydrocarbon groups such asthose groups corresponding to the above hydrocarbon groups except thatoxygen is introduced between at least part of the carbon atoms formingcarbon-carbon bonds (but oxygen atoms are not inserted contiguously),for example, alkoxyalkyl groups, alkoxyalkylene glycol groups andtetrahydrofurfuryl groups. The C₁₋₂₀ cyclic hydrocarbon groups may haveacyclic hydrocarbon moieties. Further, the acyclic hydrocarbon moietiespresent in these groups may be linear or branched.

In the case where the C₁₋₂₀ hydrocarbon groups or the C₁₋₂₀oxygen-containing hydrocarbon groups contain linear alkylene moieties,at least one of the methylene groups in such moieties may be substitutedby an ester bond, an amide bond, a carbonate bond, a urethane bond (acarbamoyl group) or a urea bond (but the methylene groups are notsubstituted contiguously).

Further, hydrogen atoms present in the organic groups such as the C₁₋₂₀hydrocarbon groups and the C₁₋₂₀ oxygen-containing hydrocarbon groupsmay be substituted by acid groups such as carboxyl groups and phosphategroups, and functional groups such as hydroxyl groups, amino groups andepoxy groups.

Examples of the methacryloyl-containing compounds represented by thegeneral formula (12) include methyl methacrylate, ethyl methacrylate,propyl methacrylate, butyl methacrylate, hexyl methacrylate, cyclohexylmethacrylate, ethoxydiethylene glycol methacrylate, methoxytriethyleneglycol methacrylate, phenoxyethyl methacrylate, 2-hydroxyethylmethacrylate, 2-hydroxypropyl methacrylate, 2-hydroxybutyl methacrylate,2-hydroxy-3-phenoxypropyl methacrylate, 4-hydroxybutyl methacrylate and1,4-cyclohexanedimethanol monomethacrylate.

Examples of the acryloyl-containing compounds represented by the generalformula (12) include methyl acrylate, ethyl acrylate, propyl acrylate,butyl acrylate, hexyl acrylate, cyclohexyl acrylate, ethoxydiethyleneglycol acrylate, methoxytriethylene glycol acrylate, phenoxyethylacrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate,2-hydroxybutyl acrylate, 2-hydroxy-3-phenoxypropyl acrylate,4-hydroxybutyl acrylate and 1,4-cyclohexanedimethanol monoacrylate.

Examples of the polymerizable compounds (B) having two or morepolymerizable groups include those polymerizable compounds representedby the general formula (13) below.

In the general formula (13), R³ and R⁴ each represent hydrogen or amethyl group and may be the same as or different from each other; and R⁵represents a C₁₋₄₀ divalent organic group which may contain oxygen ornitrogen. The dental polymerizable monomers (A) are not categorized asthe compounds represented by the general formula (13).

Examples of the divalent organic groups include hydrocarbon groups, forexample, C₁₋₄₀ acyclic hydrocarbon groups such as alkylene groups,alkenylene groups and alkynylene groups, and C₁₋₄₀ cyclic hydrocarbongroups such as cycloalkylene groups, cycloalkenylene groups,cycloalkynylene groups and arylene groups; and C₁₋₄₀ oxygen-containinghydrocarbon groups such as those groups corresponding to the abovehydrocarbon groups except that oxygen is introduced between at leastpart of the carbon atoms forming carbon-carbon bonds (but oxygen atomsare not inserted contiguously), for example, oxyalkylene groups. TheC₁₋₄₀ cyclic hydrocarbon groups may have acyclic hydrocarbon moieties.Further, the acyclic hydrocarbon moieties present in these groups may belinear or branched.

In the case where the C₁₋₄₀ hydrocarbon groups or the C₁₋₄₀oxygen-containing hydrocarbon groups contain linear alkylene moieties,at least one of the methylene groups in such moieties may be substitutedby an ester bond, an amide bond, a carbonate bond, a urethane bond (acarbamoyl group) or a urea bond (but the methylene groups are notsubstituted contiguously).

Further, hydrogen atoms present in the organic groups such as the C₁₋₄₀hydrocarbon groups and the C₁₋₄₀ oxygen-containing hydrocarbon groupsmay be substituted by acid groups such as carboxyl groups and phosphategroups, functional groups such as hydroxyl groups, amino groups andepoxy groups, and polymerizable groups such as acryloyl groups andmethacryloyl groups.

Among the polymerizable compounds represented by the general formula(13), some preferred polymerizable compounds are those polymerizablecompounds in which R⁵ is a linear alkylene group having 2 to 20 carbonatoms, desirably 4 to 12 carbon atoms.

Examples of the compounds which correspond to the above preferredpolymerizable compounds and have methacryloyl groups include1,4-butanediol dimethacrylate, 1,6-hexanediol dimethacrylate,1,8-octanediol dimethacrylate, 1,9-nonanediol dimethacrylate and1,10-decanediol dimethacrylate.

Examples of the compounds which correspond to the above preferredpolymerizable compounds and have acryloyl groups include 1,4-butanedioldiacrylate, 1, 6-hexanediol diacrylate, 1,8-octanediol diacrylate,1,9-nonanediol diacrylate and 1,10-decanediol diacrylate.

Among the polymerizable compounds represented by the general formula(13), other preferred polymerizable compounds are those polymerizablecompounds in which R⁵ is a linear oxyalkylene group having 2 to 20carbon atoms, desirably 4 to 12 carbon atoms.

Examples of the compounds which correspond to the above preferredpolymerizable compounds and have methacryloyl groups include ethyleneglycol dimethacrylate, diethylene glycol dimethacrylate, triethyleneglycol dimethacrylate, tetraethylene glycol dimethacrylate, polyethyleneglycol dimethacrylate, tripropylene glycol dimethacrylate,tetrapropylene glycol dimethacrylate and polypropylene glycoldimethacrylate.

Examples of the compounds which correspond to the above preferredpolymerizable compounds and have acryloyl groups include ethylene glycoldiacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate,tetraethylene glycol diacrylate, polyethylene glycol diacrylate,tripropylene glycol diacrylate, tetrapropylene glycol diacrylate andpolypropylene glycol diacrylate.

Among the polymerizable compounds represented by the general formula(13), other preferred polymerizable compounds are carbamoylgroup-containing polymerizable compounds represented by the generalformula (14) below. The dental polymerizable monomers (A) are notcategorized as the compounds represented by the general formula (14).

In the general formula (14), R³ and R⁴ each represent hydrogen or amethyl group and may be the same as or different from each other; and R⁶and R⁷ each represent a C₁₋₁₂ divalent organic group which may containoxygen, and may be the same as or different from each other.

Examples of the divalent organic groups include hydrocarbon groups, forexample, C₁₋₁₂ acyclic hydrocarbon groups such as alkylene groups, andC₁₋₁₂ cyclic hydrocarbon groups such as cycloalkylene groups and arylenegroups; and C₁₋₁₂ oxygen-containing hydrocarbon groups such as thosegroups corresponding to the above hydrocarbon groups except that oxygenis introduced between at least part of the carbon atoms formingcarbon-carbon bonds (but oxygen atoms are not inserted contiguously),for example, oxyalkylene groups. The C₁₋₁₂ cyclic hydrocarbon groups mayhave acyclic hydrocarbon moieties. Further, the acyclic hydrocarbonmoieties present in these groups may be linear or branched.

Further, hydrogen atoms present in the organic groups such as the C₁₋₁₂hydrocarbon groups and the C₁₋₁₂ oxygen-containing hydrocarbon groupsmay be substituted by acid groups such as carboxyl groups and phosphategroups, functional groups such as hydroxyl groups, amino groups andepoxy groups, and polymerizable groups such as acryloyl groups andmethacryloyl groups.

In the general formula (14), R⁸ represents a C₁₋₂₀ divalent organicgroup which may contain oxygen. Examples of the divalent organic groupsinclude C₁₋₂₀ acyclic hydrocarbon groups such as alkylene groups; andC₁₋₂₀ oxygen-containing hydrocarbon groups such as those groupscorresponding to the above hydrocarbon groups except that oxygen isintroduced between at least part of the carbon atoms formingcarbon-carbon bonds (but oxygen atoms are not inserted contiguously),for example, oxyalkylene groups. The C₁₋₂₀ acyclic hydrocarbon groupsmay have acyclic hydrocarbon moieties. Further, the acyclic hydrocarbonmoieties present in these groups may be linear or branched.

Further, hydrogen atoms present in the organic groups such as the C₁₋₂₀hydrocarbon groups and the C₁₋₂₀ oxygen-containing hydrocarbon groupsmay be substituted by acid groups such as carboxyl groups and phosphategroups, and functional groups such as hydroxyl groups, amino groups andepoxy groups.

Examples of the methacryloyl group-containing compounds represented bythe general formula (14) include urethane methacrylates formed by thereaction between a hydroxymethacrylate such as 2-hydroxyethylmethacrylate, 2-hydroxypropyl methacrylate, 2-hydroxybutyl methacrylate,2-hydroxy-3-phenoxypropyl methacrylate, 4-hydroxybutyl methacrylate or1,4-cyclohexanedimethanol monomethacrylate, and a diisocyanate such as2,4- or 2,6-toluene diisocyanate, 4,4′-, 2,4′- or2,2′-diphenylmethane-diisocyanate, 1,6-hexamethylene diisocyanate, or2,2,4- or 2,4,4-trimethyl-1,6-hexamethylene-diisocyanate. Examples ofsuch urethane methacrylates include 2,2,4-trimethylhexamethylenebis(2-carbamoyloxyethyl) dimethacrylate (UDMA).

Examples of the acryloyl group-containing compounds represented by thegeneral formula (14) include urethane acrylates formed by the reactionbetween a hydroxyacrylate such as 2-hydroxyethyl acrylate,2-hydroxypropyl acrylate, 2-hydroxybutyl acrylate,2-hydroxy-3-phenoxypropyl acrylate, 4-hydroxybutyl acrylate or1,4-cyclohexanedimethanol monoacrylate, and a diisocyanate such as 2,4-or 2,6-toluene diisocyanate, 4,4′-, 2,4′- or2,2′-diphenylmethane-diisocyanate, 1,6-hexamethylene diisocyanate, or2,2,4- or 2,4,4-trimethyl-1,6-hexamethylene-diisocyanate. Examples ofsuch urethane acrylates include 2,2,4-trimethylhexamethylenebis(2-carbamoyloxyethyl) diacrylate.

Among the polymerizable compounds represented by the general formula(13), other preferred compounds are those polymerizable compoundsrepresented by the general formula (15) below.

In the general formula (15), R³ and R⁴ each represent hydrogen or amethyl group and may be the same as or different from each other; and R⁹and R¹⁰ each represent a C₁₋₁₂ divalent organic group which may containoxygen, and may be the same as or different from each other.

Examples of the divalent organic groups include hydrocarbon groups, forexample, C₁₋₁₂ acyclic hydrocarbon groups such as alkylene groups, andC₁₋₁₂ cyclic hydrocarbon groups such as cycloalkylene groups and arylenegroups; and C₁₋₁₂ oxygen-containing hydrocarbon groups such as thosegroups corresponding to the above hydrocarbon groups except that oxygenis introduced between at least part of the carbon atoms formingcarbon-carbon bonds (but oxygen atoms are not inserted contiguously),for example, oxyalkylene groups. The C₁₋₁₂ cyclic hydrocarbon groups mayhave acyclic hydrocarbon moieties. Further, the acyclic hydrocarbonmoieties present in these groups may be linear or branched.

Further, hydrogen atoms present in the organic groups such as the C₁₋₁₂hydrocarbon groups and the C₁₋₁₂ oxygen-containing hydrocarbon groupsmay be substituted by acid groups such as carboxyl groups and phosphategroups, functional groups such as hydroxyl groups, amino groups andepoxy groups, and polymerizable groups such as acryloyl groups andmethacryloyl groups.

In the general formula (15), R¹ represents a C₁₋₂₀ divalent organicgroup which may contain oxygen.

Examples of the divalent organic groups include C₁₋₂₀ hydrocarbon groupssuch as alkylene groups, cycloalkylene groups and arylene groups; andC₁₋₂₀ oxygen-containing hydrocarbon groups such as those groupscorresponding to the above hydrocarbon groups except that oxygen isintroduced between at least part of the carbon atoms formingcarbon-carbon bonds (but oxygen atoms are not inserted contiguously),for example, oxyalkylene groups. The C₁₋₂₀ cyclic hydrocarbon groups mayhave acyclic hydrocarbon moieties. The acyclic hydrocarbon moietiescontained in these groups may be linear or branched.

Further, hydrogen atoms present in the organic groups such as the C₁₋₂₀hydrocarbon groups and the C₁₋₂₀ oxygen-containing hydrocarbon groupsmay be substituted by acid groups such as carboxyl groups and phosphategroups, and functional groups such as hydroxyl groups, amino groups andepoxy groups.

Examples of the methacryloyl group-containing compounds represented bythe general formula (15) include2,2-bis[4-(3-methacryloyloxy-2-hydroxypropoxy)phenyl]propane (Bis-GMA),ethylene oxide-modified bisphenol A dimethacrylate and propyleneoxide-modified bisphenol A dimethacrylate.

Examples of the acryloyl group-containing compounds represented by thegeneral formula (15) include2,2-bis[4-(3-acryloyloxy-2-hydroxypropoxy)phenyl]propane, ethyleneoxide-modified bisphenol A diacrylate and propylene oxide-modifiedbisphenol A diacrylate.

When the dental polymerizable monomer composition of the invention isused in such an application as dental adhesives, it is preferable thatthe composition contain a polymerizable compound (B) exhibiting abonding function. Examples of such adhesive polymerizable compounds (B)include those polymerizable compounds having at least one polymerizablegroup selected from methacryloyl groups and acryloyl groups, and anacidic group. Examples of the acidic groups include phosphate residues,pyrophosphate residues, thiophosphate residues, carboxylate residues andsulfonate residues.

Examples of the polymerizable compounds having a methacryloyl group anda phosphate residue include 2-methacryloyloxyethyl dihydrogen phosphate,9-methacryloyloxynonyl dihydrogen phosphate, 10-methacryloyloxydecyldihydrogen phosphate, 11-methacryloyloxyundecyl dihydrogen phosphate,20-methacryloyloxyeicosyl dihydrogen phosphate,1,3-dimethacryloyloxypropyl-2-dihydrogen phosphate,2-methacryloyloxyethyl phenyl phosphoric acid, 2-methacryloyloxyethyl2′-bromoethyl phosphoric acid, methacryloyloxyethyl phenyl phosphonate,and acid chlorides of these compounds.

Examples of the polymerizable compounds having an acryloyl group and aphosphate residue include 2-acryloyloxyethyl dihydrogen phosphate,9-acryloyloxynonyl dihydrogen phosphate, 10-acryloyloxydecyl dihydrogenphosphate, 11-acryloyloxyundecyl dihydrogen phosphate,20-acryloyloxyeicosyl dihydrogen phosphate,1,3-diacryloyloxypropyl-2-dihydrogen phosphate, 2-acryloyloxyethylphenyl phosphoric acid, 2-acryloyloxyethyl 2′-bromoethyl phosphoricacid, acryloyloxyethyl phenyl phosphonate, and acid chlorides of thesecompounds.

Examples of the polymerizable compounds having a methacryloyl group anda pyrophosphate residue include di(2-methacryloyloxyethyl)pyrophosphate, and acid chlorides thereof.

Examples of the polymerizable compounds having an acryloyl group and apyrophosphate residue include di(2-acryloyloxyethyl) pyrophosphate, andacid chlorides thereof.

Examples of the polymerizable compounds having a methacryloyl group anda thiophosphate residue include 2-methacryloyloxyethyl dihydrogendithiophosphate, 10-methacryloyloxydecyl dihydrogen thiophosphate, andacid chlorides of these compounds.

Examples of the polymerizable compounds having an acryloyl group and athiophosphate residue include 2-acryloyloxyethyl dihydrogendithiophosphate, 10-acryloyloxydecyl dihydrogen thiophosphate, and acidchlorides of these compounds.

Examples of the polymerizable compounds having a methacryloyl group anda carboxylate residue include 4-methacryloyloxyethoxycarbonylphthalicacid, 5-methacryloylaminopentylcarboxylic acid,11-methacryloyloxy-1,1-undecanedicarboxylic acid, and acid chlorides andacid anhydrides of these compounds.

Examples of the polymerizable compounds having an acryloyl group and acarboxylate residue include 4-acryloyloxyethoxycarbonylphthalic acid,5-acryloylaminopentylcarboxylic acid,11-acryloyloxy-1,1-undecanedicarboxylic acid, and acid chlorides andacid anhydrides of these compounds.

Examples of the polymerizable compounds having a methacryloyl group anda sulfonate residue include 2-sulfoethyl methacrylate and2-methacrylamido-2-methylpropanesulfonic acid.

Examples of the polymerizable compounds having an acryloyl group and asulfonate residue include 2-sulfoethyl acrylate and2-acrylamido-2-methylpropanesulfonic acid.

The dental polymerizable monomer composition of the invention mayinclude an acidic group-containing polymerizable compound which is notcategorized into the polymerizable compounds (B). Examples of suchacidic group-containing polymerizable compounds include sulfonateresidue-containing polymerizable compounds such as styrenesulfonic acid.The acidic group-containing polymerizable monomers may be used singly,or two or more may be used in combination.

When the dental polymerizable monomer composition of the inventioncontains such an acidic group-containing polymerizable compound, theacidic group-containing polymerizable compound may be added in anyamount without limitation. Usually, the dental polymerizable monomercomposition contains the acidic group-containing polymerizable compoundin such an amount that the number of the polymerizable groups present inthe acidic group-containing polymerizable compound is not more than 50%relative to the total number of the polymerizable groups in the dentalpolymerizable monomer composition.

The viscosity of the inventive dental polymerizable monomer compositionis not particularly limited, but is preferably in the range of 1 to100,000 mPa·s at 25° C., more preferably in the range of 5 to 60,000mPa·s, still more preferably in the range of 10 to 30,000 mPa·s, andfurther preferably in the range of 100 to 10,000 mPa·s. If the viscosityis above the upper limit, the dental polymerizable monomer compositiondoes not allow components such as fillers to be dispersed thereinefficiently during the production of the inventive dental composition,possibly resulting in a failure to obtain a uniform mixture. If, on theother hand, the viscosity is less than the lower limit, the dentalpolymerizable monomer composition will contain an increased amount ofair bubbles when components such as fillers are admixed therewith duringthe production of the inventive dental composition, possibly resultingin a failure to obtain a uniform mixture. The polymerizable monomercomposition is sometimes partially oligomerized during storage at hightemperatures. The viscosity discussed here is a value immediately afterthe production of the polymerizable monomer composition before theoccurrence of any oligomerization.

In the invention, the hue of the dental polymerizable monomercomposition is not particularly limited, but is preferably one suitedfor use as a raw ingredient for dental materials. Specifically, the APHAscale is preferably not more than 500, more preferably not more than200, and still more preferably not more than 100.

In the production of the inventive dental polymerizable monomercomposition, the dental polymerizable monomer (A) and the polymerizablecompound (B) may be mixed together by any method without limitation. Forexample, the inventive dental polymerizable monomer composition may beobtained by adding the dental polymerizable monomer (A) and thepolymerizable compound (B) into a container and stirring the mixture touniformity while performing heating appropriately.

To obtain an enhancement in storage stability, the dental polymerizablemonomer composition of the invention may contain the polymerizationinhibitor described hereinabove. The inhibitor may be added during thesynthesis of the dental polymerizable monomer (A) as mentionedhereinabove, or may be added during a downstream step as required.

By the addition of a polymerization initiator described later, thedental polymerizable monomer composition of the invention comes toexhibit polymerizability at normal or elevated temperatures or uponillumination. Cured products of the inventive dental polymerizablemonomer compositions have high mechanical properties as compared tocured products of conventional dental polymerizable monomercompositions, and in particular have high and well-balanced flexuralbreaking strength and fracture energy. In other words, the curedproducts are materials that exhibit both toughness and rigidity.

The dental polymerizable monomer composition of the invention mayfurther contain additives such as fungicides, disinfectants, stabilizersand preservatives as required while still ensuring that the advantageouseffects of the invention are not impaired.

[Dental Compositions]

The dental polymerizable monomer composition of the invention may besuitably used as a component for the inventive dental composition. Thedental composition includes the dental polymerizable monomer compositiondescribed hereinabove, a polymerization initiator and a filler. Thedental composition has cold- or room temperature-polymerizability,thermal polymerizability or photopolymerizability, and may be suitablyused as, for example, a dental restorative material.

The polymerization initiator may be any of general polymerizationinitiators used in the dental field, and is usually selected inconsideration of the polymerizability of the polymerizable monomers, andthe polymerization conditions. In the case of self curing, for example,a redox polymerization initiator that is a combination of an oxidant anda reductant is preferable. When using a redox polymerization initiator,an oxidant and a reductant which are separately packaged need to bemixed with each other immediately before use.

The oxidants are not particularly limited. Examples include organicperoxides such as diacyl peroxides, peroxy esters, dialkyl peroxides,peroxyketals, ketone peroxides and hydroperoxides. Examples of theorganic peroxides include such diacyl peroxides as benzoyl peroxide, 2,4-dichlorobenzoyl peroxide and m-toluoyl peroxide; such peroxy esters ast-butyl peroxybenzoate, bis-t-butyl peroxyisophthalate,2,5-dimethyl-2,5-bis(benzoylperoxy)hexane, t-butylperoxy-2-ethylhexanoate and t-butyl peroxyisopropyl carbonate; suchdialkyl peroxides as dicumyl peroxide, di-t-butyl peroxide and lauroylperoxide; such peroxyketals as1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane; such ketone peroxidesas methyl ethyl ketone peroxide; and such hydroperoxides as t-butylhydroperoxide.

The reductants are not particularly limited, but tertiary amines areusually used. Examples of the tertiary amines includeN,N-dimethylaniline, N,N-dimethyl-p-toluidine, N,N-dimethyl-m-toluidine,N,N-diethyl-p-toluidine, N,N-dimethyl-3,5-dimethylaniline,N,N-dimethyl-3,4-dimethylaniline, N,N-dimethyl-4-ethylaniline,N,N-dimethyl-4-i-propylaniline, N,N-dimethyl-4-t-butylaniline,N,N-dimethyl-3,5-di-t-butylaniline, N,N-bis(2-hydroxyethyl)-p-toluidine,N,N-bis(2-hydroxyethyl)-3,5-dimethylaniline,N,N-bis(2-hydroxyethyl)-3,4-dimethylaniline,N,N-bis(2-hydroxyethyl)-4-ethylaniline,N,N-bis(2-hydroxyethyl)-4-i-propylaniline,N,N-bis(2-hydroxyethyl)-4-t-butylaniline,N,N-di(2-hydroxyethyl)-3,5-di-i-propylaniline,N,N-bis(2-hydroxyethyl)-3,5-di-t-butylaniline, ethyl4-dimethylaminobenzoate, n-butoxyethyl 4-dimethylaminobenzoate,(2-methacryloyloxy)ethyl 4-dimethylaminobenzoate, trimethylamine,triethylamine, N-methyldiethanolamine, N-ethyldiethanolamine,N-n-butyldiethanolamine, N-lauryldiethanolamine, triethanolamine,(2-dimethylamino)ethyl methacrylate,N,N-bis(methacryloyloxyethyl)-N-methylamine,N,N-bis(methacryloyloxyethyl)-N-ethylamine,N,N-bis(2-hydroxyethyl)-N-methacryloyloxyethylamine,N,N-bis(methacryloyloxyethyl)-N-(2-hydroxyethyl)amine andtris(methacryloyloxyethyl)amine.

Besides these organic peroxide/amine systems, other redox polymerizationinitiators such as cumene hydroperoxide/thiourea systems, ascorbicacid/Cu² salt systems and organic peroxide/amine/sulfinic acid (orsulfinate salt) systems may be used. Further, other polymerizationinitiators such as tributyl borane and organic sulfinic acids are alsosuitably used.

In the case of thermal polymerization with heating, it is preferable touse peroxides or azo compounds.

The peroxides are not particularly limited, and examples include benzoylperoxide, t-butyl hydroperoxide and cumene hydroperoxide. The azocompounds are not particularly limited, and examples includeazobisisobutyronitrile.

In the case of photopolymerization with the application of visiblelights, suitable initiators are redox initiators such asa-diketones/tertiary amines, a-diketones/aldehydes anda-diketones/mercaptans.

Examples of the photopolymerization initiators, although notparticularly limited to, include a-diketones/reductants,ketals/reductants and thioxanthones/reductants. Examples of thea-diketones include camphorquinone, benzil and 2,3-pentanedione.Examples of the ketals include benzyl dimethyl ketal and benzyl diethylketal. Examples of the thioxanthones include 2-chlorothioxanthone and2,4-diethylthioxanthone. Examples of the reductants include tertiaryamines such as Michler's ketone, 2-(dimethylamino)ethyl methacrylate,N,N-bis[(meth)acryloyloxyethyl]-N-methylamine, ethylN,N-dimethylaminobenzoate, butyl 4-dimethylaminobenzoate, butoxyethyl4-dimethylaminobenzoate, N-methyldiethanolamine,4-dimethylaminobenzophenone, N,N-bis(2-hydroxyethyl)-p-toluidine anddimethylaminophenanthrol; aldehydes such as citronellal, laurylaldehyde, phthalic dialdehyde, dimethylaminobenzaldehyde andterephthalaldehyde; and thiol group-containing compounds such as2-mercaptobenzoxazole, decanethiol, 3-mercaptopropyltrimethoxysilane,4-mercaptoacetophenone, thiosalicylic acid and thiobenzoic acid. Organicperoxides may be added to these redox systems. That is,a-diketone/organic peroxide/reductant systems may be suitably used.

In the case of photopolymerization with the application of UV lights,some suitable initiators are benzoin alkyl ethers and benzyl dimethylketal. Further, such photopolymerization initiators as(bis)acylphosphine oxides are also suitably used.

Of the (bis)acylphosphine oxides, examples of the acylphosphine oxidesinclude 2,4,6-trimethylbenzoyldiphenylphosphine oxide,2,6-dimethoxybenzoyldiphenylphosphine oxide,2,6-dichlorobenzoyldiphenylphosphine oxide,2,4,6-trimethylbenzoylmethoxyphenylphosphine oxide,2,4,6-trimethylbenzoylethoxyphenylphosphine oxide,2,3,5,6-tetramethylbenzoyldiphenylphosphine oxide andbenzoyldi-(2,6-dimethylphenyl) phosphonate. Examples of thebisacylphosphine oxides include bis-(2,6-dichlorobenzoyl)phenylphosphineoxide, bis-(2,6-dichlorobenzoyl)-2,5-dimethylphenylphosphine oxide,bis-(2,6-dichlorobenzoyl)-4-propylphenylphosphine oxide,bis-(2,6-dichlorobenzoyl)-1-naphthylphosphine oxide,bis-(2,6-dimethoxybenzoyl)phenylphosphine oxide,bis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide,bis-(2,6-dimethoxybenzoyl)-2,5-dimethylphenylphosphine oxide,bis-(2,4,6-trimethylbenzoyl)phenylphosphine oxide and(2,5,6-trimethylbenzoyl)-2,4,4-trimethylpentylphosphine oxide. These(bis)acylphosphine oxide photopolymerization initiators may be usedsingly or in combination with various reductants such as amines,aldehydes, mercaptans and sulfinate salts. These reductants may besuitably used also in combination with the visible lightphotopolymerization initiators described hereinabove.

The polymerization initiators or the photopolymerization initiators maybe used singly, or two or more may be used in appropriate combination.The amount thereof is usually in the range of 0.01 to 20 wt %, andpreferably 0.1 to 5 wt % relative to the dental composition taken as 100wt %.

The filler may be any of general fillers used in the dental field. Thefillers are usually broadly categorized into organic fillers andinorganic fillers.

Examples of the organic fillers include fine powders of polymers such aspolymethyl methacrylate, polyethyl methacrylate, methylmethacrylate-ethyl methacrylate copolymer, crosslinked polymethylmethacrylate, crosslinked polyethyl methacrylate, ethylene-vinyl acetatecopolymer and styrene-butadiene copolymer.

Examples of the inorganic fillers include fine powders of inorganicsubstances such as various glasses (based on silicon dioxide andoptionally containing oxides of, for example, heavy metals, boron andaluminum), various ceramics, diatomaceous earth, kaolin, clay minerals(such as montmorillonite), activated clay, synthetic zeolite, mica,calcium fluoride, ytterbium fluoride, calcium phosphate, barium sulfate,zirconium dioxide, titanium dioxide and hydroxyapatite. Specificexamples of the inorganic fillers include barium borosilicate glasses(such as Kimble Raysorb T3000, Schott 8235, Schott GM27884 and SchottGM39923), strontium boroaluminosilicate glasses (such as Raysorb T4000,Schott G018-093 and Schott GM32087), lanthanum glasses (such as SchottGM31684), fluoroaluminosilicate glasses (such as Schott G018-091 andSchott G018-117), and boroaluminosilicate glasses containing zirconiumand/or cesium (such as Schott G018-307, G018-308 and G018-310).

In an embodiment, an organic inorganic composite filler may be usedwhich is obtained by adding a polymerizable monomer beforehand to theinorganic filler to give a paste, which is then cured by polymerizationand crushed.

In a preferred embodiment of the dental composition, the compositioncontains a microfiller having a particle diameter of 0.1 μm or less.Such a composition is suited as a dental composite resin. Preferredexamples of the materials for such micron size fillers include silica(for example, product name: AEROSIL), alumina, zirconia and titania. Theaddition of such a micron size inorganic filler is advantageous in orderfor a cured product of the composite resin to achieve high polish andsmoothness by being polished.

These fillers may have been surface treated with agents such as silanecoupling agents in accordance with purposes. Examples of such surfacetreating agents include known silane coupling agents, for example,organosilicon compounds such as γ-methacryloxyalkyltrimethoxysilanes(the number of carbon atoms between the methacryloxy group and thesilicon atom: 3 to 12), γ-methacryloxyalkyltriethoxysilanes (the numberof carbon atoms between the methacryloxy group and the silicon atom: 3to 12), vinyltrimethoxysilane, vinylethoxysilane andvinyltriacetoxysilane. The surface treating agent is usually used with aconcentration in the range of 0.1 to 20 wt %, and preferably 1 to 10 wt% with respect to 100 wt % of the filler.

The fillers may be used singly, or two or more may be used incombination appropriately. The amount of the filler may be determinedappropriately in consideration of handling properties (viscosity) of thecomposite resin paste and mechanical properties of cured products of thepaste. The amount is usually 10 to 2000 parts by weight, preferably 50to 1000 parts by weight, and more preferably 100 to 600 parts by weightwith respect to 100 parts by weight of all the components present in thedental composition except the filler.

The dental composition of the invention may contain components otherthan the inventive dental polymerizable monomer composition, thepolymerization initiator and the filler appropriately in accordance withthe purpose. For example, the composition may contain any of thepolymerization inhibitors described hereinabove in order to exhibitenhanced storage stability. To control the color tone, known colorantssuch as pigments and dyes may be added. Further, known reinforcingmaterials such as fibers may be added to increase the strength of curedproducts.

The dental composition of the invention may be cured under appropriateconditions in accordance with the manner in which the polymerizationinitiator initiates the polymerization. In the case where, for example,the inventive dental composition contains a visible lightphotopolymerization initiator, a desired cured product may be obtainedby shaping the dental composition into a prescribed form and irradiatingthe shape with visible light for a prescribed time using a knownirradiator. The conditions such as intensity and dose may be controlledappropriately in accordance with the curability of the dentalcomposition. The cured product that has been cured by the application oflight such as visible light may be heat treated under appropriateconditions, and thereby the mechanical properties of the cured productcan be enhanced.

The cured products from the inventive dental composition that areobtained as described above may be suitably used as dental materials.

The dental composition of the invention may be used by any known methodsgenerally adopted for dental materials without limitation. When, forexample, the inventive dental composition is used as a composite resinfor filling carious cavities, the purpose may be fulfilled by filling acavity in the mouth with the dental composition and photocuring thecomposition using a known irradiator. When used as a crowning compositeresin, the composition may be shaped into an appropriate form,photocured with a known irradiator and heat treated under prescribedconditions to give a desired crown material.

The cured products that are obtained from the inventive dentalcompositions including the inventive dental polymerizable monomercompositions have high mechanical properties as compared to curedproducts from conventional dental compositions containing conventionaldental polymerizable monomer compositions, and in particular exhibithigh flexural breaking strength. The detailed reasons as to why thecured products of the inventive dental compositions have high mechanicalproperties are not fully understood. In the dental composition or inparticular a composite resin as a typical example, the major proportionof the weight of the composition is accounted for by the polymerizablemonomer composition and the filler, and therefore these two componentshave a very high influence on the mechanical properties of the compositeresin cured products. In general, an inorganic filler has a far higherstrength than a cured product of the dental polymerizable monomercomposition. In contrast, the cured product of the inventive dentalpolymerizable monomer composition has excellent flexibility. Thus, inthe composite resin cured product, the inorganic filler may beconsidered as a hard segment component and the cured product as a softsegment component. In such a system, blindly increasing the rigidity ofthe soft segment component does not lead to an enhancement in themechanical properties of the composite resin cured product or ratheroften results in a hard but brittle material. As far as the soft segmentcomponent is concerned, it is probable that increasing the toughnessthereof while maintaining a certain level of rigidity will contribute toenhancing the mechanical properties of the composite resin curedproduct. When cured, the dental polymerizable monomer composition of theinvention gives a material having toughness and rigidity by virtue ofits containing the dental polymerizable monomer (A) with the specificstructure. Such a cured product is suited as the soft segment componentin the composite resin cured product, and has high mechanical propertiesand, in particular, will exhibit high flexural breaking strength.

The dental composition of the invention may be suitably used as a dentalmaterial. Examples of such materials include dental restorativematerials, denture base resins, denture base liners, impressionmaterials, dental luting materials (resin cements, resin glass ionomercements), dental bonding materials (orthodontic bonding materials,cavity-coating bonding materials), dental fissure sealants, CAD/CAMresin blocks, temporary crowns and artificial tooth materials.

The dental composition of the invention may be suitably used also as adental restorative material. The dental restorative materials areclassified by application into categories such as dental crown compositeresins, composite resins for filling carious cavities, composite resinsfor making dental abutments, and restorative composite resin fillers. Byvirtue of their high mechanical properties, the cured products of theinventive dental compositions are particularly suited for use as dentalcrown composite resins.

EXAMPLES

The present invention will be described in further detail based onExamples hereinbelow without limiting the scope of the invention to suchExamples.

The following is the abbreviations of compounds used in Examples of theinvention.

TEGDMA: triethylene glycol dimethacrylateUDMA: 2,2,4-trimethylhexamethylenebis(2-carbamoyloxyethyl)dimethacrylateHEA: 2-hydroxyethyl acrylate2HPA: 2-hydroxypropyl acrylate2HBA: 2-hydroxybutyl acrylate4HBA: 4-hydroxybutyl acrylateHPMA: 2-hydroxypropyl methacrylateXDI: 1,3-xylylene diisocyanateNBDI: norbornene diisocyanateDBTDL: dibutyltin dilaurateBHT: dibutylhydroxytolueneCQ: camphorquinoneDMAB2-BE: 2-butoxyethyl 4-(dimethylamino)benzoate

[Bending Test]

The bending test method used in Examples and Comparative Examples in theinvention will be described below.

(Fabrication of Bending Test Pieces Including Dental PolymerizableMonomer Compositions)

0.5 Parts by weight of CQ and 0.5 parts by weight of DMAB2-BE were addedto 100 parts by weight of a dental polymerizable monomer compositionfrom any of Examples and Comparative Examples. The mixture was stirredto uniformity at room temperature to give a photopolymerizable monomersolution. The photopolymerizable monomer solution was added into a2×2×25 mm stainless steel mold and was irradiated with light from avisible light irradiator (Solidilite V manufactured by SHOFU INC.) for 3minutes on each side, namely, for a total of 6 minutes on both sides.The test piece was removed from the mold and was heat treated in an ovenat 110° C. for 15 minutes. The test piece was removed from the oven andwas cooled to room temperature. Thereafter, the test piece was soaked indistilled water in a closable sample bottle and was stored at 37° C. for24 hours. The test piece thus obtained was subjected to testing.

(Fabrication of Bending Test Pieces Including Dental Compositions)

A photopolymerizable monomer solution was provided which included 100parts by weight of a dental polymerizable monomer composition from anyof Examples and Comparative Examples, 0.5 parts by weight of CQ and 0.5parts by weight of DMAB2-BE. To the solution, 300 parts by weight ofsilica glass (Fuselex-X (TATSUMORI LTD.)) was added. The mixture wasstirred to uniformity in a mortar and was degassed to give a dentalpolymerizable composition. The dental polymerizable composition obtainedwas added into a 2×2×25 mm stainless steel mold and was irradiated withlight from a visible light irradiator (Solidilite V manufactured bySHOFU INC.) for 3 minutes on each side, namely, for a total of 6 minuteson both sides. The test piece was removed from the mold and was heattreated in an oven at 110° C. for 15 minutes. The test piece was removedfrom the oven and was cooled to room temperature. Thereafter, the testpiece was soaked in distilled water in a closable sample bottle and wasstored at 37° C. for 24 hours. The test piece thus obtained wassubjected to testing.

(Bending Test)

The test pieces fabricated in the above manners were subjected to athree-point bending test with a tester (AUTOGRAPH EZ-S manufactured byShimadzu Corporation) under conditions in which the distance between thesupports was 20 mm and the cross head speed was 1 mm/min. In Table 2,the values in parenthesis in the sections of flexural breaking strengthand fracture energy indicate increases or decreases in % relative to thevalues measured in Comparative Example 1.

[Viscosity Method]

In Examples and Comparative Examples of the invention, the viscosity wasmeasured with a cone-plate viscometer (TVE-22H manufactured by TOKISANGYO CO., LTD.). The temperature was controlled at 25° C. with use ofa circulation thermostatic tank.

The viscosity in Production Examples of the invention was measured withthe above cone-plate viscometer while controlling the temperature at 65°C. with use of a circulation thermostatic tank.

Production Example 1

A thoroughly dried 1-liter four-necked flask equipped with a stirringblade and a thermometer was loaded with 418 g (3.21 mol) of 2HPA, 0.72 gof DBTDL (0.1 wt % relative to the total weight of 2HPA and XDI) and0.36 g of BHT (0.05 wt % relative to the total weight of 2HPA and XDI).The mixture was stirred to uniformity and was thereafter heated to 60°C. Subsequently, 303 g (1.61 mol) of XDI was added dropwise over aperiod of 1 hour. The dropwise addition was accompanied by an increasein inside temperature due to the reaction heat, and thus the rate of thedropwise addition was controlled so that the temperature did not exceed80° C. After the whole amount had been added dropwise, the reaction wasperformed for 10 hours while keeping the reaction temperature at 80° C.During this process, the progress of the reaction was tracked by HPLCanalysis to determine the end point of the reaction. The product wasdischarged from the reactor. In this manner, 690 g of a urethaneacrylate represented by the following formula was obtained. Theviscosity at 65° C. was 570 mPa·s. The result is described in Table 1.

Production Example 2

A thoroughly dried 1-liter four-necked flask equipped with a stirringblade and a thermometer was loaded with 390 g (3.36 mol) of HEA, 0.74 gof DBTDL (0.1 wt % relative to the total weight of HEA and NBDI) and0.37 g of BHT (0.05 wt % relative to the total weight of HEA and NBDI).The mixture was stirred to uniformity and was thereafter heated to 60°C. Subsequently, 346 g (1.68 mol) of NBDI was added dropwise over aperiod of 1 hour. The dropwise addition was accompanied by an increasein inside temperature due to the reaction heat, and thus the rate of thedropwise addition was controlled so that the temperature did not exceed80° C. After the whole amount had been added dropwise, the reaction wasperformed for 10 hours while keeping the reaction temperature at 80° C.During this process, the progress of the reaction was tracked by HPLCanalysis to determine the end point of the reaction. The product wasdischarged from the reactor. In this manner, 700 g of a urethaneacrylate represented by the following formula was obtained. Theviscosity at 65° C. was 930 mPa·s. The result is described in Table 1.

Production Example 3

A thoroughly dried 1-liter four-necked flask equipped with a stirringblade and a thermometer was loaded with 390 g (2.70 mol) of 2HBA, 0.67 gof DBTDL (0.1 wt % relative to the total weight of 2HBA and NBDI) and0.34 g of BHT (0.05 wt % relative to the total weight of 2HBA and NBDI).The mixture was stirred to uniformity and was thereafter heated to 60°C. Subsequently, 278 g (1.35 mol) of NBDI was added dropwise over aperiod of 1 hour. The dropwise addition was accompanied by an increasein inside temperature due to the reaction heat, and thus the rate of thedropwise addition was controlled so that the temperature did not exceed80° C. After the whole amount had been added dropwise, the reaction wasperformed for 12 hours while keeping the reaction temperature at 80° C.During this process, the progress of the reaction was tracked by HPLCanalysis to determine the end point of the reaction. The product wasdischarged from the reactor. In this manner, 620 g of a urethaneacrylate represented by the following formula was obtained. Theviscosity at 65° C. was 2030 mPa·s. The result is described in Table 1.

Production Example 4

A thoroughly dried 1-liter four-necked flask equipped with a stirringblade and a thermometer was loaded with 390 g (2.70 mol) of 4HBA, 0.67 gof DBTDL (0.1 wt % relative to the total weight of 4HBA and NBDI) and0.34 g of BHT (0.05 wt % relative to the total weight of 4HBA and NBDI).The mixture was stirred to uniformity and was thereafter heated to 60°C. Subsequently, 278 g (1.35 mol) of NBDI was added dropwise over aperiod of 1 hour. The dropwise addition was accompanied by an increasein inside temperature due to the reaction heat, and thus the rate of thedropwise addition was controlled so that the temperature did not exceed80° C. After the whole amount had been added dropwise, the reaction wasperformed for 8 hours while keeping the reaction temperature at 80° C.During this process, the progress of the reaction was tracked by HPLCanalysis to determine the end point of the reaction. The product wasdischarged from the reactor. In this manner, 630 g of a urethaneacrylate represented by the following formula was obtained. Theviscosity at 65° C. was 360 mPa·s. The result is described in Table 1.

Production Example 5

A thoroughly dried 1-liter four-necked flask equipped with a stirringblade and a thermometer was loaded with 390 g (2.70 mol) of 2HBA, 0.64 gof DBTDL (0.1 wt % relative to the total weight of 2HBA and XDI) and0.34 g of BHT (0.05 wt % relative to the total weight of 2HBA and XDI).The mixture was stirred to uniformity and was thereafter heated to 60°C. Subsequently, 254 g (1.35 mol) of XDI was added dropwise over aperiod of 1 hour. The dropwise addition was accompanied by an increasein inside temperature due to the reaction heat, and thus the rate of thedropwise addition was controlled so that the temperature did not exceed80° C. After the whole amount had been added dropwise, the reaction wasperformed for 8 hours while keeping the reaction temperature at 80° C.During this process, the progress of the reaction was tracked by HPLCanalysis to determine the end point of the reaction. The product wasdischarged from the reactor. In this manner, 600 g of a urethaneacrylate represented by the following formula was obtained. Theviscosity at 65° C. was 520 mPa·s. The result is described in Table 1.

Production Example 6

A thoroughly dried 1-liter four-necked flask equipped with a stirringblade and a thermometer was loaded with 195 g (1.35 mol) of HPMA, 195 g(1.35 mol) of 4HBA, 0.64 g of DBTDL (0.1 wt % relative to the totalweight of HPMA, 4HBA and XDI) and 0.32 g of BHT (0.05 wt % relative tothe total weight of HPMA, 4HBA and XDI). The mixture was stirred touniformity and was thereafter heated to 60° C. Subsequently, 254 g (1.35mol) of XDI was added dropwise over a period of 1 hour. The dropwiseaddition was accompanied by an increase in inside temperature due to thereaction heat, and thus the rate of the dropwise addition was controlledso that the temperature did not exceed 80° C. After the whole amount hadbeen added dropwise, the reaction was performed for 8 hours whilekeeping the reaction temperature at 80° C. During this process, theprogress of the reaction was tracked by HPLC analysis to determine theend point of the reaction. The product was discharged from the reactor.In this manner, 600 g of a urethane acrylate represented by thefollowing formula was obtained. The viscosity at 65° C. was 190 mPa·s.The result is described in Table 1.

[Table 1]

Example 1

10.0 g (22.3 mmol) of the urethane acrylate obtained in ProductionExample 1 and 4.81 g (16.8 mmol) of TEGDMA were added into a container.The mixture was stirred to uniformity at 50° C. to give a dentalpolymerizable monomer composition. In this case, the urethane acrylatefrom Production Example 1 had two acryloyl groups and TEGDMA had twomethacryloyl groups. Thus, the proportion of the number of the acryloylgroups present in the dental polymerizable monomer (A), namely, theurethane acrylate from Production Example 1 was 57% relative to thetotal number of the polymerizable groups in the dental polymerizablemonomer composition, and the ratio of the acryloyl groups to themethacryloyl groups in the composition was 57:43. The viscosity at 25°C. of the dental polymerizable monomer composition obtained was measuredto be 560 mPa·s.

74 mg (0.5 wt %) of CQ and 74 mg (0.5 wt %) of DMAB2-BE were added to14.81 g of the dental polymerizable monomer composition, and the mixturewas stirred to uniformity at room temperature to give a monomersolution. A cured product of the monomers was subjected to the bendingtest. The result is described in Table 2.

Examples 2 to 6

Dental polymerizable monomer compositions were obtained in the samemanner as in Example 1 using the urethane acrylates described in Table 1and additional polymerizable monomers. The results of measurements ofviscosity at 25° C. of the dental polymerizable monomer compositions andthe results of bending tests of the cured products are described inTable 2.

Example 7

A dental composition in the form of a uniform paste was obtained byadmixing 300 parts by weight of a filler (Fuselex-X), 0.5 parts byweight of CQ and 0.5 parts by weight of DMAB2-BE to 100 parts by weightof the dental polymerizable monomer composition obtained in Example 1.Table 3 describes the results of the bending test with respect to acured product of the dental composition.

Example 8

A dental composition was obtained in the same manner as in Example 7except that the dental polymerizable monomer composition from Example 1was replaced by the dental polymerizable monomer composition fromExample 2. Table 3 describes the results of the bending test withrespect to a cured product of the dental composition.

Comparative Example 1

A dental polymerizable monomer composition was obtained in the samemanner as in Example 1 except that the urethane acrylate from ProductionExample 1 was replaced by the equimolar amount of UDMA. The bending testwas performed in the same manner as in Example 1, the results beingdescribed in Table 2.

Comparative Example 2

A dental composition in the form of a uniform paste was obtained in thesame manner as in Example 7 except that the dental polymerizable monomercomposition from Comparative Example 1 was used. Table 3 describes theresults of the bending test with respect to a cured product of thedental composition.

The results in Table 2 have shown that the cured products of theinventive dental polymerizable monomer compositions achieved asignificant enhancement in flexural breaking strength and fractureenergy as compared with the cured products of the conventional dentalpolymerizable monomer compositions. That is, the cured products of theinventive dental polymerizable monomer compositions have beendemonstrated to be materials exhibiting both toughness and rigidity.

Further, the results in Table 3 have shown that the cured products fromthe dental compositions containing the inventive dental polymerizablemonomer compositions achieved a marked enhancement in flexural breakingstrength as compared to the cured products of the conventional dentalcompositions. Thus, it has been demonstrated that the incorporation ofthe inventive dental polymerizable monomer compositions having bothtoughness and rigidity enhances the flexural breaking strength of thecured products of the dental compositions.

TABLE 2 Results of bending test with respect Viscosity of to curedproducts of polymerizable polymerizable monomer compositions monomerFlexural Additional composition Elastic breaking Fracture Dentalpolymerizable polymerizable (mPa · s modulus strength energy monomers(A) monomers (B) (25° C.)) (GPa) (MPa) (mJ) Ex. 1 Pro. Ex. 1/57 mol %TEGDMA/43 mol % 560 3.2 136 (+32%) 63 (+47%) Ex. 2 Pro. Ex. 2/57 mol %TEGDMA/43 mol % 910 2.6 129 (+25%) 66 (+53%) Ex. 3 Pro. Ex. 3/63 mol %TEGDMA/37 mol % 2670 2.4 120 (+17%) 63 (+47%) Ex. 4 Pro. Ex. 4/63 mol %TEGDMA/37 mol % 750 2.1 105 (+2%)   87 (+102%) Ex. 5 Pro. Ex. 5/64 mol %TEGDMA/36 mol % 1130 2.8 123 (+19%) 58 (+35%) Ex. 6 (Pro. Ex. 6/57 mol%)*¹ TEGDMA/43 mol % 420 2.5 115 (+12%) 79 (+84%) Comp. Ex. 1 (UDMA/57mol %)*² TEGDMA/43 mol % 340 2.3 103 43 The values in parenthesis in thesections of flexural breaking strength and fracture energy indicateincreases or decreases in % relative to the values measured inComparative Example 1. *¹The amount in mol % of the mixture of urethaneacrylate and urethane methacrylate from Production Example 6 in thecomposition *²The amount in mol % of UDMA present in the composition.

TABLE 3 Flexural Flexural Dental polymerizable elastic breaking monomercompositions modulus (GPa) strength (MPa) Ex. 7 Ex. 1 15.7 217 Ex. 8 Ex.2 14.8 217 Comp. Ex. 2 Comp. Ex. 1 14.8 176

1. A dental polymerizable monomer (A) comprising a urethane acrylatethat has at least one acryloyl group and is represented by the generalformula (1) below:

wherein in the general formula (1), R^(a) is a group which has adivalent C₆₋₉ aromatic hydrocarbon group or a divalent C₆₋₉ bridgedcyclic hydrocarbon group in the middle and is bonded to nitrogen atomsin adjacent carbamoyl groups via an unsubstituted methylene group; R^(b)and R^(c) are each independently a C₂₋₆ linear alkylene group or a C₂₋₆linear oxyalkylene group, each of which is optionally substituted with aC₁₋₃ alkyl group or a (meth)acryloylmethylene group in place of ahydrogen atom; and R^(d) represents a hydrogen atom or a methyl group.2. The dental polymerizable monomer (A) according to claim 1, wherein inthe general formula (1), R^(d) is a hydrogen atom.
 3. The dentalpolymerizable monomer (A) according to claim 1, wherein in the generalformula (1), R^(a) is a group represented by the formula (2) or (3)below


4. The dental polymerizable monomer (A) according to claim 3, wherein inthe general formula (2), R^(a) is a group represented by the formula (4)below


5. The dental polymerizable monomer (A) according to claim 1, whereinR^(b) and R^(c) in the general formula (1) independently at eachoccurrence represents a C₂₋₆ linear alkylene group or a C₂₋₆ linearoxyalkylene group, each of which is optionally substituted with a C₁₋₃alkyl group in place of a hydrogen atom.
 6. A dental polymerizablemonomer composition comprising the dental polymerizable monomer (A)described in claim
 1. 7. The dental polymerizable monomer compositionaccording to claim 6, wherein the viscosity at 25° C. is 1 to 100,000mPa·s.
 8. A dental composition comprising the dental polymerizablemonomer composition described in claim 6, a polymerization initiator anda filler.
 9. A dental material obtained by curing the dental compositiondescribed in claim 8.